Earth’s deep sea
The barreleye: a fish with a see-through head
The barreleye has one of the strangest heads in the ocean: a clear, fluid-filled dome, with two glowing green eyes inside it looking up. It lives in the dim water of the Pacific, and for decades scientists only knew it from damaged specimens in nets, until they filmed one alive.
Quick facts
- Scientific name: Macropinna microstoma, one of the barreleyes (also called spookfish).
- Size: about 15 cm long.
- Depth: roughly 600 to 800 metres.
- Where: the North Pacific, from the Bering Sea to Baja California and off Japan.
- First described: 1939.
A transparent shield
The top of the barreleye’s head is a soft, clear shield filled with fluid. The two green domes you can see inside it are its eyes. The two dark spots above its mouth, which look like eyes in photos, are actually its nostrils.
Nets usually destroyed the delicate shield, which is why early drawings of the fish missed it.
Eyes that turn
Its eyes are tubes, very sensitive to light, topped with green lenses that probably filter out faint sunlight from above so the fish can spot the glow of other animals. For years people thought the eyes could only stare straight up.
In 2009, researchers at the Monterey Bay Aquarium Research Institute filmed living barreleyes and showed that the eyes can rotate inside the shield to look forward, so the fish can watch its food as it eats.
What it eats
Barreleyes hang almost still in the water, using their large fins to stay steady. They seem to eat small drifting animals, and scientists think they may steal food caught in the stinging tentacles of siphonophores (long colonial relatives of jellyfish), with the clear shield protecting their eyes.
Relatives with mirrors
Other barreleyes and spookfish have tube eyes too. One, the brownsnout spookfish, has a second set of eyes that use mirrors made of crystals to focus light: the only animal with a backbone known to see this way.
Glass fish in Fish of Ganymede
In the game, glass-bodied fish with telescope eyes are a nod to the barreleye. You can breed for both traits and see the fish’s skeleton glowing through its clear body. See real fish patterns and glass fish or start playing.
Questions
Is the barreleye fish real?
Yes. Macropinna microstoma lives in the North Pacific, roughly 600 to 800 metres deep, and has been filmed alive by research submarines.
Why is the barreleye’s head transparent?
Its head is covered by a clear, fluid-filled shield. It lets light reach the upward-looking eyes, and may protect them from stinging prey.
More guides
The real deep-sea fish behind our alien fishThe strangest real deep-sea creatures: anglerfish, dragonfish, the gulper eel, barreleyes and hatchetfish. How they hunt, glow and survive in the dark.
Hatchetfish: deep-sea mirrors and river fliersTwo very different hatchetfish: silver deep-sea fish that hide with belly lights, and freshwater hatchetfish that can leap out of the water. Facts and size.
The gulper eel: a deep-sea fish that is mostly mouthThe gulper eel, or pelican eel, is a deep-sea fish with a huge, loosely hinged mouth and a glowing tail. Where it lives, what it eats and how big it gets.